Electric circuits



Bu D. BEDFORD ELECTRIC CIRCUIT Aug. 6, 1946.

Filed Feb. 12, 1945 5 Sheets-Sheet 1 m @uw Mb H His @Iter-neg.

23mg. 6, "19460 E., n. BEDFQR@ 294652397 l ELECTRIC CIRCUIT Filed Feb.12', 19345 3 sheetsfsheet 2.

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Burnice D. Bedford, b9 //My MIM-1 His Attorney.

Auvg. 6, 1946. B. D. BEDFORD 2,405,397

l ELECTRIC CIRCUIT Filed Febr 12, 194s s sheets-sheet ls Fig.

Inventor: Burnce D. Bedford,

b5 ,JW

Hi8 Attorneg.

Patented Aug. 6, 1,946

ELECTRIC CIRCUITS Burnice D. Bedford, Schenectady, N. Y., assignor toGeneral Electric Company, a corporation of New York Application February12, 1943, Serial No. 475,645

13 Claims. 1

My invention relates to electric control and indicating circuitsparticularly adapted for use in connection with electric valve means forindieating abnormal operation thereof.

Electrical apparatus employing electric valves of the type utilizing anionizable medium has been extensively used in industrial applications.These electric valves, which normally conduct in one direction only,sometimes conduct in the reverse direction. The reverse current isusually many times larger than the normal forward current and has causedconsiderable operating difculty in systems of this type. From thestandpoint of the operator, it is desirable to know which valve arcsback first in order that it may be removed from the system andreconditioned in the event that it fails persistently. From thestandpoint of design, it is desirable to know in addition the time inthe anode-cathode voltage wave that the arc-back occurs since thisinformation is of assistance in determining the' cause of the arc-backand the features of design which may be modified to eliminate the fault.In accordance with the teachings of my invention, I provide new andimproved electric circuits for indicating which one of a number oftransients, such as those caused by arc-back of an electric valve meansoccurs rst' and further for indicating the time in the cycle of theanode-cathode voltage of the valve means at which the arcback occurs.

It is an object of my invention to provide a new and improved electriccircuit for indicating the rst of a plurality of transient conditions.

It is another object of my invention to provide a new and improvedelectric indicating circuit for indicating the instant in theanode-cathode voltage wave that an electric valve conducts in thereverse direction.

It is another object of my inventio-n to provide an improved electriccircuit for indicating the rst of a plurality of electric valves toconduct in a reverse direction and to record the time in theanode-cathode voltage of the valve that reverse conduction is initiated.I

In accordance with the illustrated embodiments of my invention, animproved electromagnetic device is associated with each of the anodeconductors of an electric valve system to produce an impulse of voltageupon the occurrence of an arc-back in the associated electric valve. Anindicating circuit having a controlled electric valve and an indicatingdevice in series for each electric valve of the power system is providedand each of the controlled electric valves is energized in accordancewith the voltage produced by the electromagnetic device associated witha corresponding one of the main electric valves. When any one of thecontrolled valves conducts in response to an arc-back in thecorresponding main valve, the remainder of the controlled electricvalves are prevented from operating. An auxiliary circuit associatedwith each of the main electric valves and controlled in response toconduction of any one of the controlled electric valves of the indicatorcircuit provides means for indicating the time in the anode-cathodevoltage wave at which the arc-back occurs. In

' accordance with another illustrated embodiment one of theelectromagnetic devices employed inA the embodiment illustrated in Fig.1, Fig. 3 represents certain operating characteristics of the circuitillustrated in Fig. l, and Figs. 4 and 5 are schematic diagrams of otherembodiments of my invention.

Referring now to Fig. 1 of the drawings, I have shown my inventionembodied in an indicating circuit applied to an electric valvetranslating apparatus connected between a polyphase alternating-currentcircuit li) and a direct-current circuit comprising conductors Il andl2. In the following description it will be assumed that the electricvalve apparatus is operating as a rectier, in which case, the circuit H3is the supply circuit and the conductors Il and I2 constitute the loadcircuit. lIhe translating apparatus includes a transformer i3 havinggroups of electrically displaced secondary windings I4 and I5 havingneutral connections interconnected by an interphase transformer If. Thephase terminals of the windings I4 and i5 are connected with thedirect-current conductor I2 through electric valves il to 22, inclusive.A midpointon the interphase transformer i6 is connected with the otherdirect-current conductor il. Each of the electric valves, asillustrated, comprises an anode `23, a cathode 2i, and animmersion-ignitor control member 2R. In order to simplify the drawings,no energizing circuits for control member have been illustrated and itwill be understood that any of the types of control known. in the' artmay be used, if desired.

I provide an indicating circuit including a plurality of parallelelectric paths, the number ci paths corresponding to the number ofelectric valves in the rectifier system. lllhe electric paths areenergized in parallel across conductors 26 and 21 and each comprises anindicating device such as an electric lamp 2S and a controlled electricvalve. The valves, as indicated by the dot within the envelope, are ofthe gaseous type and are designated by numerals 29 to til, inclusive,and correspond respectively to the main electric valves ll to 22,inclusive. The other valves of the various illustrated embodiments whichare of the gaseous type are similarly indicated. As a means forenergizing the conductors 26 and 27, I provide a full-wave rectierenergized from a transformer 3c having the primary winding 3l thereofconnected with the alternating-current supply circuit it. The output ofthe rectiner is filtered by a se ies reactor 33 and parallel capacitorand impresse on Voltage-dividing resistors eil and ll through a manualswitch e2. The conductor 26 is connected with one terminal of theresistor fill and the conductor 2l is connected with the common terminalof resistors Ml and ll through a resistor 0,3 and a manual switch 43.

In order to provide a source ci control voltage for the electric valves29 to 30, dependent upon an arc-back condition in the electric valves ilto 22, respectively, I provide a plurality-of electromagnetic devicesillustrated generally by the numeral lit, and one of which is associatedwith the anode conductor of each of the electric valves, Referringbriefly to Fig. 2, each of the electromagnetic devices comprises aclosed magnetic circuit Alli including oppositely disposed legs Il@ andil of smaller cross section than the connecting end portions of thecore. Control windings 43 and 49 are Wound on the legs it and dll,respectively, and direct-current saturating windings 50 and 5l arepositioned on the legs l and It? on the outside of the control windingsl and 139. As illustrated in the drawings, the directcurrent coils lilland 5l of each device Ml are connected in series. Referring again toFig. 1, it will be noted that the direct-current windings of the devicesM associated with the anode conductors of all of the electric valves areconnected in series and energized from a source of direct current whichmay be derived from the transformer winding 36 by means of a full-waverectier 52. The control windings i8 and t9 are connected in parallel andone common. terminal thereof is connected to the control member of thecorresponding electric valve 23 through a resistor 53. The other commonterminal of the control winding is connected to the negative terminal ofvoltage-dividing resistor Il! which provides a source oi negative biasfor the electric valve 29 and, as previously mentioned, is connected tothe cathode thereof through switch t3 and resistor dit. A capacitor 5eis connected between the control member and cathode of each. of theelectric valves 29 to The control windings of the device it associatedwith main electric valve ll are the only ones that have shown connectedin the drawings, It will be understood that the control windings of theremaining devices associated with valves i3 to are d similarly connectedin the control-to-cathode circuit of electric valves 3@ to 3e.

Before describing the operation of the indicating circuit, thearrangement provided in Fig. l for indicating the time in theanode-cathode voltage cycle of each of the electric valves ll to 22 atwhich an arc-back occurs will be described. Associated with the valvesil to inclusive, are the control circuits to ll respectively. Thesecircuits are identical and the same reference numerals will be employedto designate the corresponding parts and only one will be described.Referring to the circuit i a resistance a nonlinear and a portion ofresistance which provi es a source` of unidirectional voltage areconnected in series across the anode-cathode circuit of th electricvalve il, The resista-nce elements preferably of the type having anegative-current impedance characteristic so that the voltage across theterminals thereof is maintained substantially constant. These resistanceelements may be formed of a material disclosed. and claimed in UnitedStates Patent 1,822,742, granted September 8, 1931, of Karl B. McEachronand assigned to the assignee of the present invention.. The voltageappearing across the nonlinear resistance element 62 is utilized forcharging a capacitance Elf through a resistance Gli in accordance withthe inverse voltage of the electric Valve ll. An electric valve d5, aninductive element El', and a capacitance til are connected in seriesacross the capacitor te. The electric valve lid is of the type employingan ionizable medium, as indicated by the dot within the envelope, and isprovided with a control member its which is energized by a secondarywinding l@ of the transformer il to render the electric valve conductiveat the instant one of the main electric valves arcs back. This isaccomplished by energizing the primary winding l2 of the transformer inaccordance with the voltage appearing across resistor da which, as willbe brought out in more detail at a later point in the specification,impresses a transient voltage on the winding 'l2 at the time that thefirst one of these electricl valves t9 to becomes conductive. Acapacitor i3, connected in series with Winding l2, prevents steady-statedirect current from flowing in the primary winding l2. The voltage dropappearing across the upper portion of resistor (i3 is adjusted by theslider le so as to be equal substantially to the normal arc drop of theelectric valve El' and the electric valve et, The voltage for energizingthe resistor Eis may be obtained in any suitable manner and is derivedfrom the output of a rectifier bridge l5 energized from a transformer ltwhich may, in turn, be energized from any suitable source of alternatingcurrent, such as the supply circuit it. A capacitor 'll' connected inparallel with resistor 33 provides a lowimpedance path for transientvoltages and mits the rapid discharge oi the condenser t`=l duringconduction of the valve il through a path which includes the resistor diand the anodecathode circuit of the valve il. A unilateraly conductingdevice 'lis is connected in parallel with resistor and is poled toprovide a second discharge path -for capacitor fill during theconducting pericd of the electric valve il. As will become more apparentafter a description of the operation of the system described above, themagnitude of the charge on the condenser Et after an arc back will be anindication of the time in the anode-cathode voltage wave of theassociated main electric valve at which the arcback occurred. In orderto measure this voltage, I provide a measuring instrument, such as agalvanometer 19, which may be selectively connected in circuit with thecapacitor 68 of circuits 55 to 60 by means of manual switches 85 to 85,respectively.

A better understanding of the features and advantages of my inventionmay be had by a brief consideration of the operation of the system as awhole. Let it be assumed that the electric valves I1 to 22 are operatingnormally as a. double three-phase rectifier to supply unidirectionalcurrent to the conductors Il and l2. The electromagnetic devices 44associated with the anode leads of the electric valves l1 to 22 aresaturated suiciently as a result of the unidirectional current owing inthe windings 5i! and 5I so that the decay of current through theassociated electric valves during normal operation induces only a smallvoltage in the control windings 48 and 49. The negative biaseslimpressed on the electric valves 29 to 34 by resistor 4I together withthe time constant of the circuit including resistor 53 and capacitor 54cooperate to maintain the valve nonconductive during this operation. Ifelectric valve I1, for example, conducts current in a reverse direction,the change in iiux in the core 45 will be many times that occasioned bythe normal decay of current through the electric valve l1 when itbecomes nonconducting. A relatively large impulse of voltage is inducedin the windings 43 and 49 and this is impressed on the control member ofelectric valve 29 and the associated indicating lamp 28 is energized.From an inspection of the drawings, it will be noted that conduction ofany one of the valves 29 to 34 will increase the negative bias impressedon the control members of the remaining valves by resistor 4l andresistor 43 and, assuming that resistor 43 is substantially smaller thanresistor 45, will simultaneously decrease the anode-cathode voltage ofthese valves appearing between conductors 26 and 21. This increase -innegative bias and decrease in anodecathode voltage is suiicient toprevent more than one of the electric valves 29 to 34 from becomingconductive regardless of the number of main electric valves which arcback. Thus, only the rst arc back to occur is indicated.

In the above discussion, it was pointed out that all of thedirect-current windings are connected in series and the control windingsare located on opposite legs of the device 44 and connected in parallel.This arrangement of windings has numerous advantages. With the controlwindings connected directly in parallel, there is etsablished alow-impedance closed circuit including these two coils so that anytendency for there to be a change in iiux in one leg without acorresponding change in flux in the same direction in the other leg isopposed by a circulating current in the low-impedance circuit whichsubstantially prevents any quick change in flux in the two legs inopposite directions due to stray flux from other phases of the system.This arrangement of windings and the relatively large cross section ofthe core legs between the winding legs prevents false operation of theindicating system due to stray flux not symmetrically located withrespect to the coils. The series connection of the direct-currentwindings provides considerable impedance in the direct-current circuitand minimizes the effect of transient voltages in this circuit.

When the electric valves l1 to 22 are operating normally, the capacitor64 is periodically charged during the inverse-voltage cycle anddischarged quickly at the end of this voltage cycle. The voltage acrossresistor 63 is employed to insure an initial charge on the capacitor 64at the beginning of the inverse-voltage cycle corresponding to thebreak-down voltage of the electric valve 65. Referring particularly toFig. 3, the inverse voltage of electric valve l1 is illustrated by curveA. Curve B illustrates the voltage across the nonlinear resistance 62with the initial negative voltage being determined by the setting of theslider 14 on resistor 63. curve C illustrates the voltage of thecapacitor 64, which may be operated over such a range that the increasein voltage is substantially linear. At the end of the inverse-voltagecycle. the voltage on the condenser is rapidly discharged as illustratedat D through the unilaterally conducting device 18. In the event that anarcback occurs in electric valve l1 at any time during theinverse-voltage cycle, the electric valve 2'9 is rendered conductive anda transient voltage appears across resistor 43. This voltage throughtransformer 1| renders each of the electric valves 66 of circuits 55 to60, inclusive, conductive and the charges on capacitors 64 aretransferred to the corresponding capacitors 68 through the anode-cathodecircuits of the associated valves 66. The inductance 61 renders thedischarge circuit of capacitor 64 oscillatory to insure reversal of theanode-cathode voltage of valve 6E a termination of its conduction. Thecapacitor 68 having no discharge circuit established for it will holdits charge for a cornparatively long period of time. The operator, uponobserving from the lamps 28 that one of the electric valves has arcedback may close one of the switch B to S5 corresponding to the firstvalve to arc back and read the deflection of the galvanometer 19 todetermine the time during the inverse-voitage cycle that the arc-backoccurred. It is apparent that calibration charts may be made for anygiven voltage of the system so that the deflection of the galvanometermay be converted to a phase position of the arc back. In order to resetthe system for a subsequent operation, the control electric valves 28 to3L! may all be rendered nonconducting by opening switch 42 or 43 toremove the anode-cathode voltage and the capacitors 68 may be completelydischarged by temporarily closing the manual switches 8i) to 85,inclusive.

In Fig. 4, I have illustrated a modioation of my .invention in which adifferent arrangement for recording the time in the inverse-voltagecycle at which the arc-back occurred is provided. The system forindicating which one of the various 'phases arc-s back iirst is the sameas that de.-

scribed in connection with'Fig. l and corresponding parts have beendesignated by the same reference numerals. In the arrangement shown inFig. 4, the time in the inverse-voltage cycle at which the arc-backoccurs is recorded on a disk by means of an electrical impulse which isproduced when the arc-back occurs. This disk is rotated synchronouslywith the voltage of the supply circuit in the sense that the Cycles ofoperation of the disk and the alternations of the voltage of the supplycircuit bear a timed relation to each other. Referring now to Fig. 4. arotating disk 86 is mounted on the shaft or a synchronous motor 81 whichis energized from the alternating-current supply circuit I5 through Thedotted a transformer 88. The disk is preferably of good conductingmaterial and is provided with a central hub 89 which is electricallyconnected with one terminal of the transformer winding 99a by means of abrush contact 91. The other terminal of the winding a is connectedthrough a resistor 92 with a recording electrode 93 which is held inproximity to the rotating disk by any suitable means not shown. Animpulse is produced in the Winding sila upon the occurrence of anarc-back in any one of the electric valves Il to 21?. by means of acircuit illustrated generally by the numeral Iifi. The circuit .filiincludes an electric discharge device 95 which is connected in serieswith the primary winding iib of the transformer Sti and across thevoltage-dividing resistor I0 through manual switches 95 and Ii'I. Aresistor 98 is also connected in this circuit. An energy-storagecapacitor .'Ii is connected across the electric valve 95 and the seriesconnected transformer winding glib to be charged from the resistor Allthrough resistor 9B. The control member of the electric valve Q isconnected with the cathode thereof through the resistor 98, a capacitorIi, and resistor EIII. The common terminal of capacitor le@ and resistorI @i is connected through manual switch I32 with the negative terminalof resistor i I. With this arrangement, the control member of theelectric valve is maintained at the poten-- tial of the negativeterminal cf resistor II when the electric valve system including valvesI'I to is operating normally. The capacitor SQ is charged to the fullvoltage appearing across resistor di). A5 pointed out in connection withthe operation of the arrangement of Fig, 1, the voltage across resistorIl is reduced and the voltage across resistor 4I is increased at theinstant any of the electric valves 29 to 34 are rendered conductive inresponse to an arc-back in a corresponding one of the main electricvalves I'I to 22. This momentarily renders the control member oi' thevalve 95 positive with respect to the cathode thereof and eifectsdischarge of capacitor Sii through the transformer winding 9% and, as aresult, causes a spark to jump from the electrode 93 the disk 33 and, inthis way, forms a hole in the paper chart IIlS which is secured on theface of the disk 36 in any desired manner.

In order that the hole in the paper will indicate the time in theinverse-voltage cycle that the arc-back occurs, I provide means forsynchronizing the disk 88 with the inverse-voltage cycle of the electricvalves Il to 22. As illustrated in the drawings, the disk is providednear the edge thereof with an opening les behind which is mounted a lampm5, which may be supported in any suitable manner, and which isenergized in accordance with the voltage across a resistor H255. Theresistor IE5 is connected in series with parallel connected resistorlIi'i capacitor ISS and across the anode-cathode circuit of the electricvalve Il. The constants of the circuit including resistors IBS and IQ'Iand the capacitor I t8 are so chosen that the lamp is illuminated onlyduring the rapid change of voltage across the electric valve Iloccurring at the beginning of the inverse-voltage cycle. In this way,the lamp is made to iiash at the beginning of the inverse-voltage cycleand, by adjusting the disk on the shaft of the motor or adjusting thephase of the voltage impressed on the motor windings, a definitereference or zero position of the disk may be established. Inasmuch asthe phase relation of the voltages of all of the electric valves isknown with respect to the voltages of the valve I'I, the instant ofarc-back in the inverse-voltage cycle of any of the valves may readilybe determined.

In Fig. 5, I have illustrated another embodiment of my invention inwhich the occurrence of an arc-back in any one of the main electricvalves is recorded and in which means are provided for indicating whichof the valves arcs back first. In Fig. 5, the power system is the sameas that described and illustrated in Fig. 1 and the same referencenumerals have been used to designate corresponding parts. In thearrangement shown in Fig. 5, the electromagnetic devices associated withthe anode conductors of each of the elec-tric valves may be the same asthose described in connection with Fig. 1. However, as illustrated inFig. 5, these devices, designated by the numerals |89 to I I4, eachincludes only a single control winding I I5 and a single saturatingwinding Il. One terminal of each of the contro-l windings is connectedto a common conductor Ill which is, in turn, connected with the hub I Itof a rotating disk I I9 through a brush contact i223. The otherterminals of the windings I I5 are connected with recording electrodesI2! to IZB, inclusive, through suitable current-limiting resistors I2'I.An additional electrode I28 is connected with the conductor I I'Ithrough the secondary winding |529 of a transformer I 3u, the primarywinding ISI of which is energized only upon the occurrence of the firstarc-back by a control -circ it illustrated generally by the numeral I32.

'I'he saturating winding Il@ of the devices I to lis, inclusive, areconnected in series and for energization from the conductors |33 and|34'.

which are energized by direct current from the output terminals cf arectifier bridge |35. The bridge E35 may be energized from thealternating-current supply circuit Iii through the transformer I whichalso provides a source of power for the motor I3? which drives therecording disk IIS. Across the terminals of each of the saturatingwindings III is connected a resistance element |33 so that, upon theoccurrence of an arc-back in any one of the main electric valves Il' to22, the transient voltage produced across one of the resistors isimpressed on the conductors ist and i3d through a noninductive circuit.This impulse of voltage is impressed on the primary winding Ide of atransformer Iii@ through a capacitor is! to render conductive anelectric valve MZ. The valve M2 has the control member thereof connectedwith the secondary winding I I3 of the transformer winding IM! through asuitable current-limiting resistor Ilili and the anode-cathode circuitthereof connected in series with the primary winding I SI of transformerIfiii and a capacitor Ii which has been charged through resistors I diiand l-II'I from the directcurrent supply conductors IEE and Lili.

The operation of the embodiment of my invention illustrated in Fig.5-may be briey described as follows. When the electric valves Il to Z2are operating normally, the voltages induced in the windings of devicesIt to IIIi, inclusive, are relatively small and no sparks are caused tojump from the recording electrodes to the rotating disk. Upon theoccurrence of an arc-back, a Voltage impulse of large magnitudeI isinduced in the winding I I5 of the electromagnetic device associatedwith the valve which has failed and a spark is caused tor pass from thecorresponding electrode to the rotating disk IIII. At they same instant,the voltage impulse induced in the saturating winding IIS is impressedon the transformer Winding |39 and renders electric Valve |42 conductiveto discharge condenser |45 through the transformer |30 and thereby tocause a spark to jump from the electrode |28 to the revolving disk ||9.Inasmuch as all of the recording electrodes are supported in alignmenton a radius of the disk ||9, there will be tvvo holes in the recordpaper upon the occurrence of the iirst arc-back and only one hole foreach arc-back occurring thereafter, if the disk |I9 is rotated at arelatively slow speed, it may be lpossible to record all the arc-backsoccurring in one sequence before the chart makes a complete revolution.It will be readily appreciated that the arrangement shown in Fig. may beoperated to indicate or record the time in the inverse voltage cycle atwhich the arc-back occurs by synchronizing the position of the disk I9with the inverse voltage cycle of one of the main electric valve meansl1 to 22 in the same manner as described in detail in connection withFig. 4.

Although resistors 33 have been shown connected across windings H6, itwill be obvious to those skilled in the art that rectiiiers suitablypoled may replace such resistors Without departing from my invention.

While I have shown and described particular embodiments of my invention,it Will be obvious to those skilled in the art that changes andmodifications may be made Without departing from my invention in itsbroader aspects, and I, therefore, aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of VtheUnited States is:

l. In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals ancl for subjecting said valve means to an inverse voltagecycle during each of the normally nonconductingV intervals, saidelectric valve means being subject to an arcback during said inversevoltage cycle, an energy storage device, means for supplying electricenergy to said energy storage device, means including an electricdischarge device connected to be rendered conductive in response to theoccurrence of an arc-back in said electric valve means for releasing theenergy ofsaid energy storage device, and means connected to be energizedin accordance with the release of energy of said energy storage devicefor determining the instant in the inverse voltage cycle that anarc-back in said electric valve means occurs.

2. In combination, an electric valve means, means for rendering saidelectric Valve means conducting and nonconducting during predeterminedintervals and for subjecting said valve means to an inverse voltagecycle during each of the normally nonconducting intervals, said electricvalve means being subject to an arcback during said inverse voltagecycle, means including an energy storage device for producing anelectric quantity which varies progressively in accordance with theduration of the inverse voltage cycle, means responsive to the magnitudeof said electric quantity at the instant of an arcback for indicatingthe time in the inverse voltage cycle that the arc-back occurs.

3. In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals and for subjecting said valve means to an inverse voltagecycle during each of the normally nonconducting intervals, a capacitor,means for charging said capacitor in accordance with the inverse voltagecycle, and means responsive to the condition of charge of said capacitorupon the occurrence of an arcback for indicating the time in the inversevoltage cycle that the arc-back occurs.

4. In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals and for subjecting said valve means to an inverse Voltagecycle during each or" the normally nonconducting intervals, a capacitor,means for charging said capacitor in accordance with the inverse voltagecycle impressed on said valve means, a second capacitor, means fortransferring the charge from said first capacitor to said secondcapacitor upon the occurrence of an arc-back, and means for measuringthe vcharge on said second capacitor to indicate the time in the inversevoltage cycle that the arcback occurs.

5. In combination, a plurality of electric valve means, means forenergizing said electric valve means to render said valve meansalternately conducting and nonconducting in a predetermined sequence andfor subjecting each of said valve means to an inverse voltage cycleduring the normally nonconducting periods thereof, each of said electricvalve means being subject to arcback during said inverse voltage cycle,capacitance means associated with each of said plurality of electricvalve means and having a charge and discharge circuit, current supplymeans connected to said charge circuit for charging said capacitancemeans, means including an electric discharge device interposed in thedischarge circuit of said capacitance means and connected to be renderedconductive in response to the occurrence of an arc-back in said electricvalve means for discharging said capacitance means, and means connectedto be energized in accordance with an electrical condition o thedischarge circuit of said capacitance means for determining the instantin the inverse voltage cycle 0I" the faulty electric valve means atWhich arc-back occurs.

6, In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals and for subjecting said valve eans to an inverse voltage cycleduring each of the normally nonconducting intervals, said electric valvemeans being subject to an abnormal operating connection during saidinverse Voltage cycle, a capacitor, means for charging said capacitorbetween predetermined limits during each inverse voltage cycle, meansfor discharging said capacitor upon the occurrence of said abnormaloperating condition, and means responsive to the charge on saidcapacitor at the instant that an abnormal operating condition of saidvalve means occurs for indicating the time in the inverse voltage cyclethat said abnormal condition occurs.

7. In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals and for subjecting said Valve means to an inverse vo-ltagecycle during each of the normally nonconducting intervals, a capacitor,means for charging said capacitor in accordance with the inverse voltagecycle impressed on said Valve means, a second capacitor, an electricvalve including a control member interconl ll necting said capacitors,means for rendering said electric valve conductive upon the occurrenceof an abnormal condition of said electric valve means for transferringthe charge from said rst capacitor to said second capacitor upon theoccurrence of said abnormal condition, and means for measuring thecharge of said second capacitor to indicate the time in the inversevoltage cycle that the abnormal condition occurs.

8. In combination, an electric valve means, means for rendering saidvalve means conductive and nonconductive during predetermined intervalsand for subjecting said valve means to an inverse voltage cycle duringeach of the normally nonconducting intervals, a record chart, means formoving said chart at a predetermined speed relative to the frequency ofthe voltage applied to said valve means, means operatively associatedwith said record chart for indicating a reference point for said chartcorresponding to the instant of initiation of inverse voltage cycle, andmeans for recording on said chart the instant that an arc-back in saidvalve means occurs relative to said reference point.

9. In combination, an electric valve means, means for rendering saidelectric valve means conducting and nonconducting during predeterminedintervals and for subjecting said valve means to an inverse voltagecycle during each of the normally nonoonducting intervals, a recordchart, means for moving said record chart at a predetermined speedrelative to the frequency of the Voltage applied to said valve means,means operatively associated with said record chart for indicating areference point for said chart corresponding to the instant ofinitiation of said inverse voltage cycle of said electric valve means,and means including means for producing a voltage impulse upon theoccurrence of an abnormal condition in said electric valve means forindicating o-n said chart the instant in the inverse voltage cyclerelative to said reference point that said abnormal condition occurs.

l0. In combination, a plurality of electric Valve means, means includingan alternating-current circut for energizing said electric valve meansto render said valve means alternately conduct'- ing and nonconductingin a predetermined sequence, a record chart, means for moving saidrecord chart in a predetermined timed relation with the frequency ofsaid alternating-current circuit, means associated with said chart forindicating on said chart the instant that any of said Valve means arcsback, and additional means for recording on said chart the instant ofinitiation of said inverse cycle so as to establish a point of referenceon said chart for determining the nrst electric valve means to arc back.

1l. In combination, a plurality of electric valve means, means inclucingan alternating-current circuit for energizing said electric valve meansto render said valve means alternately conducting and nonconducting in apredetermined sequence, a record chart, means for moving said recordchart in a predetermined timed relation with the frequency of saidalternating-current circuit, a plurality of electrodes associated withsaid char", means for impressing an impulse of Voltage on apredetermined one of said electrodes when a corresponding one of saidelectric valve means arcs back, an additional electrode, and means forimpressing an impulse of voltage on said additional electrode only whenthe first of said electric valve means arcs back.

12. In combination, an electromagnetic device having a closed core ofsubstantially rectangular shape with tivo oppositely located legs ofsubstantially smaller cross section than the remaining two oppositelydisposed legs, a Winding on each of said legs of smaller cross section,means for energizing said windings with unidirectional current toproduce substantial saturation of said legs of smaller cross section, asecond windon each of said legs ci smaller cross section, means forconnecting said second windings in parallel, and means responsive tosaid parallel connected windings for indicating a transient electricalcondition in a cond ctor symmetrically located with respect to said legsof smaller cross section, said legs of larger rro-ss section and saidparallel connected windings operating to'prevent operation of saidtransient-indicating means in response to stray magnetomotive forces notsymmetrically located with respect to said legs of smaller crosssection.

13. In combination, a plurality of circuits normally subjected to acyclically recurring electrical condition, a plurality ofelectromagnetic devices arranged one with each of said circuits and eachelectromagnetic device including a core structure and a first winding oneach of said core structures and each Winding being coupled with one ofsaid circuits, a plurality of indicating means each individual to one ofsaid circuits, means connecting rst windings respectively With saidindicating means, a second winding on each of said core structures, adirect-current supply means, means connecting said second windings inseries and for energization from said direct-current supply means, andmeans responsive to a transient voltage in the series direct currentcircuit of said second windings resulting from a voltage induced in oneof said second windings in response to a transient voltage in one cisaid circuits for indicating the rst transient voltage to occur in oneof said circuits.

BURNICE D. BEDFORD.

